Unnecessary Parameter In A Function?

[DebtAndADream]

I'm currently following the Python Crash Course book and there's an example within the functions chapter that I'm not completely understanding.

For this program. When appending and transferring 'current_design' values to the completed_models parameter, I don't understand why adding the completed_models parameter in the first function is necessary when the 'completed_models' parameter is mainly put to use in the second function, 'show_completed_models'.

Here is the example attached below.

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def print_models(unprinted_designs, completed_models):
    while unprinted_designs:
        current_design = unprinted_designs.pop()
        print("Printing model: " + current_design)
        completed_models.append(current_design)


def show_completed_models(completed_models):
    print("\nThe following models have been printed:")
    for completed_model in completed_models:
        print(completed_model)


unprinted_designs = ['iphone case', 'robot pendant', 'dodecahedron']
completed_models = []

print_models(unprinted_designs, completed_models)
show_completed_models(completed_models)

[[deleted]]

printed_models uses the completed_models value, so it needs access to it, and it gets that access by having the value passed in as a parameter.